Back to EveryPatent.com
United States Patent |
5,127,059
|
Elion
,   et al.
|
June 30, 1992
|
Audio amplifiers
Abstract
A pre-amplifier for musical instrument audio signals which utilizes a solid
state programmable logic device to control a plurality of solid state
switches for routing the audio signals in preselected manner through
successive stages of vacuum tube amplification.
Inventors:
|
Elion; Clifford S. (Van Nuys, CA);
Robinson; John M. (Tujunga, CA)
|
Assignee:
|
Gibson Guitar Corp. (Nashville, TN)
|
Appl. No.:
|
467735 |
Filed:
|
January 18, 1990 |
Current U.S. Class: |
381/120; 381/61; 381/98 |
Intern'l Class: |
H03F 021/00; H03G 003/00 |
Field of Search: |
381/61,63,120,98,103
|
References Cited
U.S. Patent Documents
4495640 | Jan., 1985 | Frey | 381/98.
|
4701957 | Oct., 1987 | Smith | 381/61.
|
4935875 | Jun., 1990 | Hayashi | 381/63.
|
Other References
The Audio Cyclopedia by H. M. Tremaine, 1980, pp. 548-550, Model LA-2A
leveling amplifier.
Noll, FET Principles, Experiments, and Projects, 1975, pp. 221-223.
Lancaster, CMOS Cookbook, 1979, pp. 349-355.
|
Primary Examiner: Isen; Forester W.
Attorney, Agent or Firm: Laney, Dougherty, Hessin & Beavers
Claims
What is claimed is:
1. An improved audio signal pre-amplifier comprising:
an analog signal audio input;
solid state amplifier and switching circuitry receiving said analog signal
audio input and producing a predetermined mix of analog audio output
signals;
a programmable array logic device programmed to produce a plurality of
control outputs for control of said solid state switching circuitry; and
a vacuum tube amplifier having at least one vacuum tube receiving said
analog audio output signals to produce an audio pre-amplifier output, said
vacuum tube amplifier comprising plural successive vacuum tube stages and
a dual triode output amplifier with cathode follower output.
2. An audio signal pre-amplifier as set forth in claim 1 wherein said
plural successive vacuum tube stages are further characterized to include:
a first dual vacuum tube amplifier receiving a first switching input and
providing a first stage cathode follower output;
a second vacuum tube amplifier receiving a second switching input and
providing a second stage output; and
a third vacuum tube amplifier receiving a third switching input and
providing a third stage output for input to said dual triode output
amplifier.
3. An audio signal pre-amplifier, comprising:
an analog signal input;
a programmable array logic device programmed to produce a plurality of
control outputs;
first solid state amplifier and switching circuitry responsive to at least
one of said control outputs for receiving said analog signal input and
generating a first analog output;
a first vacuum tube amplifier receiving said first output and producing a
first stage output;
second solid state switching circuitry controlled by selected ones of said
control outputs to receive first stage output and produce plural channels
of selectively treated second analog signals;
a second vacuum tube amplifying said plural channels of second analog
signals to produce a second stage output;
third solid state switching circuitry controlled by selected ones of said
control outputs to receive second stage output and produce plural,
selectively treated third analog signals;
a third vacuum tube amplifying said third analog signals to produce a third
stage output; and
output means receiving said third stage output and producing an analog
audio signal output.
4. An audio signal pre-amplifier as set forth in claim 3 wherein said
output means comprises:
a fourth vacuum tube amplifier receiving said third stage output and
producing a fourth output analog signal; and
a cathode follower stage receiving said fourth output analog signal and
producing said analog audio signal output.
5. An audio signal pre-amplifier, comprising:
input means for receiving an analog signal;
means, connected to said input means, for providing at least three
differently conditioned analog signals in response to an analog signal
received by said input means;
first vacuum tube means for providing a first stage analog output signal;
a plurality of switches for connecting one of the at least three
differently conditioned analog signals to said first vacuum tube means so
that the first stage analog output signal is responsive to the connected
signal;
means for providing at least three channels of conditioning of the first
stage analog output signal;
means for providing a pre-amplifier analog output signal in response to one
of the at least three channels of conditioned first stage analog output
signal, including:
means for providing a second stage analog output signal, including second
vacuum tube means;
means for providing a third stage analog output signal, including third
vacuum tube means; and
a plurality of switches interconnecting the at least three channels of
conditioned first stage analog output signal with said second vacuum tube
means and said third vacuum tube means; and
digital control circuit means, connected to both said pluralities of
switches, for controlling both said pluralities of switches so that the
pre-amplifier analog output signal is one of at least three differently
conditioned versions of the analog signal received by said input means.
6. An audio signal pre-amplifier as set forth in claim 5, wherein said
digital control circuit means includes a single programmable array logic
device.
7. An audio signal pre-amplifier as set forth in claim 6, wherein said
means for providing a pre-amplifier analog output signal further includes:
means for providing differently conditioned third stage analog output
signals;
fourth vacuum tube means for providing the pre-amplifier analog output
signal in response to one of the differently conditioned third stage
analog output signals; and
a further plurality of switches, responsive to said digital control circuit
means, for selectably connecting one of the differently conditioned third
stage analog output signals to said fourth vacuum tube means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates generally to an improved audio preamplifier of the
type used for receiving input of stringed instruments and, more
particularly, but not by way of limitation, it relates to an audio
switching and amplifying apparatus wherein solid state logic circuitry
control signal amplification through multiple vacuum tube stages.
2. Description of the Prior Art
The use of vacuum tubes in musical instrument amplifiers and pre-amplifiers
is quite old and well-known. Indeed, all amplifiers prior to the advent of
solid state amplifiers in the late 1950's were constructed utilizing hard,
vacuum tube technology. By the same token, solid state logic circuitry and
programmable logic technology in general is quite commonplace today in
digital electronics and particularly in digital computer design. However,
Applicant does not know and has been unable to discover any teachings that
would combine the two approaches, i.e., the use of programmable solid
state logic circuitry in con-junction with vacuum tube amplifier design
for music audio reproduction.
SUMMARY OF THE INVENTION
The present invention relates to improvements in vacuum tube amplifier
control and fidelity by using programmable solid state logic circuitry in
combination therewith. A programmable logic device provides sequenced
output command pulses to logic switching circuitry which controls signal
routing, gain control and signal combining through three vacuum tube gain
stages. Output from the three gain stages is then applied through a
multi-channel volume and tone control array whereupon the signal is input
to a final output amplifier stage with cathode follower output to the next
stages.
Therefore, it is an object of the present invention to provide a
pre-amplifier for selectively providing multi-channel output of distinctly
different instrument sounds.
It is also an object of the present invention to provide a pre-amplifier
for guitar output signals that provides more efficient switching between
channels and sounds.
It is still another object of the invention to enable a speaker contour
filter for simulating the frequency response of a typical guitar speaker
cabinet.
Finally, it is an object of the present invention to provide a logic
controlled multi-channel pre-amplifier offering distinct sound selection
and having provision for multiple effects loops.
Other objects and advantages of the invention will be evident from the
following detailed description when read in conjunction with the
accompanying drawings which illustrate the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of the programmable logic circuitry of the
present invention;
FIG. 2 is a schematic diagram of first stage amplifier of the invention;
FIG. 3 is a schematic diagram of the second and third stage amplifiers of
the present invention; and
FIG. 4 is a schematic diagram of the power output stage of the programmable
pre-amplifier.
DETAILED DESCRIPTION OF THE INVENTION
Referring to FIG. 1, the logic control circuitry includes a programmable
array logic device 10 that functions to control the front panel and foot
switch decode logic for the pre-amplifier. Programmable logic device 10 is
controlled by a clock generator, an op-amp oscillator 12 (type LN324AN)
providing a clock pulse output on lead 14, e.g., 50 to 60 Hertz, for input
to pin 1 of logic device 10. Other inputs applied to logic device 10 are
CH3BOOST at pin 2, BUTTON at pin 3, FS1 at pin 4, and FS2 at pin 5
(footswitch inputs). A reset is input at pin 6 while CH2BOOST is input at
pin 7. Pin 8 receives input of a delay signal from an op-amp comparator 22
(type LN324AN) via lead 24 and this signal effects a mute time-out.
Program control outputs from logic device 10 include a mute output on pin
19 and lead 26 for input to the delay comparator 22. Pin 18 provides a
CHANNEL 1 output on lead 28 which is applied through a type 2N3904
transistor 30 to produce an ASW2 output (analog switch 2). Lead 28 is also
applied to the base of yet another type 2N3904 transistor 32 to produce a
CHISNK output (CHANNEL 1 turn-on) on collector output lead 34. Pin 17
provides output on lead 36 to a type 2N3904 transistor 38 which generates
ASW1 output on lead 40. Pin 16 of logic device 10 provides output on a
lead 42 to the base of another similar type transistor 44 to produce
CHIIISNK output on lead 46, and output lead 42 is also applied to energize
an op-amp 48 to generate SLOSTART signal as output on lead 50. Finally,
output pin 15 of logic device 10 connects to a lead 52 that is dually
connected to the base of a type 2N3904 transistor 54 to generate ASW3
output at lead 56 and it is connected to the base of a similar transistor
58 to generate CHIISNK output on lead 60. An output 62 is diode connected
to respective output leads 34 and 60 to conduct a BRTLED signal that is
used to energize LED indicators throughout the circuitry.
The program for the programmable array logic device 10 is as follows:
______________________________________
/** Inputs **/
Pin 1 = CLK ; /*System clock - approx 5 ms. */
Pin 2 = CHA3DRIVE ; /*Front Panel DRIVE PULL
switch */
Pin 3 = !BUTTON ;/*Front Panel select button */
Pin 4 = SWA ; /*Footswitch bit0 */
Pin 5 = SWB ; /*Footswitch bitl */
Pin 6 = !RESET ; /*Not reset */
Pin 7 = CHA2DRIVE ; /*Front panel DRIVE PULL
switch */
Pin 8 = DELAY ; /*Mute timeout input */
/** Outputs **/
Pin 12
= Q0 ; /*Machine */
Pin 13
= Q1 ; /*State */
Pin 14
= Q2 ; /*State */
Pin 15
= CHANN2 ; /*OP1,3 */
Pin 16
= CHANN3 ; /*OP2,6,ASW1 */
Pin 17
= DRIVE ; /*Selects DRIVE Circuit */
Pin 18
= CHANN1 ;
Pin 19
= MUTE ; /*Starts mute timeout by strobing
one-shot */
/** Declarations and Intermediate Variable Definitions **/
field. ampstate + [Q2..0]; /* State variables */
$define
CH1wt `b` 000
$define
CH1 `b` 001
$define
CH2wt `b` 010
$define
CH2 `b` 011
$define
CH3wt `b` 100
$define
CH3 `b` 101
$define
ResetS `b` 111
$define
BadState `b` 110
field switch = [SWA,SWB];
toch1 = switch:[`b` 01];
/* Channel 1 */
toch2 = switch:[`b` 10];
/* Channel 2 */
toch3 = switch:[`b` 00];
/* Channel 3 */
/** Logic Equations **/
condition
if RESET out Q0.d out Q1.d out Q2.d out MUTE.d;
sequence ampstate
Present ResetS
if !RESET next CH1wt out MUTE.d out !DRIVE.d;
if RESET next ResetS;
present CH1wt
Out !CHANN1.d out !CHANN2.d out !CHANN3.d;
if (BUTTON # DELAY) next CH1wt;
if !(BUTTON # DELAY)
next CH1;
present CH1
out CHANN1.d out !CHANN2.d out !CHANN3.d;
if BUTTON # toch2 next CH2wt out MUTE.d;
if toch3 next CH3wt out MUTE.d;
if !(BUTTON # toch2 # toch3)
next CH1;
present CH2wt
out !CHANN1.d out !CHANN2.d out !CHANN3.d;
if BUTTON # DELAY next CH2wt;
if !(BUTTON # DELAY)
next CH2;
present CH2
out !CHANN1.d out CHANN2.d out !CHANN3.d;
if !CHA2DRIVE out Drive.d;
if BUTTON # toch 3 next CH3wt out MUTE.d;
if toch1 next CH1wt out MUTE.d;
if !(BUTTON # toch1 # toch3
next CH2;
Present CH3wt
out !CHANN1.d out 1chann2.d out !CHANN3.d;
if BUTTON # DELAY next CH3wt;
if !(BUTTON # DELAY)
next CH3;
present CH3
out !CHANN1.d out !CHANN2.d out CHANN3.d;
if !CHA3DRIVE out DRIVE.d;
if BUTTON # toch1 next CH1 wt out MUTE.d;
if toch2 next CH2wt out MUTE.d;
if !(BUTTON # toch1 # toch2)
next CH.sub.3 ;
______________________________________
FIG. 2 illustrates the input and first stage of the preamplifier. An input
signal may be received at input jack 70 and/or a rear panel input 72,
e.g., an auxiliary input for guitar or synthesizer. Such input is
amplified in a solid state amplifier 74 (type TL074N QUAD AMP) whereupon a
clamped output is derived on lead 76 for output to a tuner or other
external means. Various types of external "effects" circuitry or devices
may be utilized at this point for altering selected ones of sound
characteristics. Signal is returned to the rear panel for input via lead
77 as it is applied as a clamped input to the positive terminal of a
quad-amp 78 (type TL074N). The output of transistor amplifier 78 is then
present on lead 80 for application to opposite inputs of amplifiers 82 and
84 (type TL074N) which function to amplify effects return signals from
external equipment. A branch output 86 from amplifier 78 is applied to a
FET switch 88 (CD4053) as the output lead 90 from effects return
transistor 84 is applied to the other contact of FET switch 88 while a
common output 92 is connected to a contact of an FET switch 94 (CD4053).
The remaining contact of switch 94 is connected to output lead 95 from the
remaining effects return amplifier 82. The control leads 96 and 98 receive
respective inputs ASW1 and ASW2 to actuate the analog switches thereby to
control input on a grid lead 100.
A first amplifier stage consists of dual triode 102a and 102b, a type 12AX7
vacuum tube. Output on lead 100 from analog switch 94 is applied to the
grid of triode 102a as the cathode is connected to an R/C parallel
combination to ground and the plate is connected through a load resistor
104, 106 to B+ voltage. Output from triode 102a is taken from junction 108
for application to the grid of triode 102b. Triode 102b is then connected
as a cathode follower to provide a stage 1 output on lead 110.
Referring now to FIG. 3, there are shown the second and third gain stages
as they interact with various switching and control circuitry. The stage 1
output present on lead 110 is applied in parallel through a CHANNEL 1
volume potentiometer 112, a CHANNEL 2 gain potentiometer 114 and a CHANNEL
3 gain potentiometer 116. Outputs from potentiometers 114 and 116 on
respective leads 118 and 120 are controlled by opto-switches 122 and 124,
respectively. The opto-switches are a type VT5C1. The respective light
sources of the opto-switches 122 and 124 are controlled by current
conduction on leads 126 and 128 which cause illumination of the unit light
source.
Thus, it is in the second stage input circuitry where the audio signal is
separately processed to bring about three audio channels, CHANNELS 1, 2
and 3, having different signal characteristics. The channels may select
the following, for example:
CHANNEL 1--"clean" guitar sounds;
CHANNEL 2--"CRUNCH" sounds; and
CHANNEL 3--"lead/overdriven" sounds.
A front panel pushbutton switch 130 provides a BUTTON output which is
applied as input to pin 3 of logic device 10 (FIG. 1). Front panel ganged
button switches 132 and 134 provide control of CH2BOOST and CH3BOOST,
respectively, and button switch 136 connects CHIISNK with lead 138 to
actuate the opto-switch 140. The switches 132/134 are a ganged switch type
K12214 SW.
The second and third gain stages are made up of respective halves 142a and
142b of a dual triode, a 12A.times.7 type vacuum tube. The CHANNEL 2 gain
output lead 118 is applied to the grid 144 of triode 142a as the cathode
is connected through an R/C bias network to ground. The plate is connected
through load resistance 146 to the B+ supply and output is taken from
plate junction 148 via lead 150. Second stage output from opto-switch 140
is applied to grid lead 152 of the third gain stage triode 142b. The grid
lead 152 is also connected through an opto-switch 154 to a lead 156 which
is the output of the CHANNEL 1 volume control potentiometer 112.
Analog switch output from logic device 10, viz. ASW3, is input at lead 158
to control actuation of a FET switch 160 (type CD4053) that changes the
cathode to ground impedance of second gain stage triode 142a. Harmonic
drive can be varied by control of pushbutton ganged switches 162 and 164
(type K12214 SW) as they function in conjunction with opto-switch 166 to
decouple between the plate output lead 168 and the grid lead 152 of third
gain stage triode 142b. Thus, the output lead 168 constitutes the stage 3
output.
Referring now to FIG. 4, stage 3 output on lead 168 is prepared for further
logic coupling and input to a final power output amplifier consisting of
triode halves 170a and 170b, a 12AU7 type vacuum tube. Signal on lead 168
is applied through series-connected tone control potentiometers 172, 174
and 176, treble, bass and mid-range, respectively. The output signal on
wiper lead 178 is then subjected to volume control potentiometer 180 and
applied on lead 182 to opto-switch 184.
A parallel portion of stage 3 output on lead 168 is conducted in a CHANNEL
3 mode where it is acted upon by tone control potentiometers 186, 188 and
190, treble, bass and mid-range, respectively. Tone adjusted output on
lead 192 then passes through volume control potentiometer 194 and wiper
output 196 is applied to opto-switch 198. Thus, with SLOSTART providing
current return, the signal CHISNK (FIG. 1) activates opto-switch 184 and
output signal is present on lead 200 to grid lead 202 and the grid of
triode 170a to provide CHANNEL 1 output. Wiper output from volume control
potentiometer 180 on a lead 204 is applied through an opto-switch 206, and
application of a CHIISNK signal (FIG. 1) activates opto-switch 206 and
provides CHANNEL 2 output on lead 200 and grid lead 202 for amplification
in power output stage 170a. Finally, CHANNEL 3 output on lead 196 from
volume control potentiometer 194 is switched through opto-switch 198 on
application of the CHIIISNK signal (FIG. 1) to produce output on lead 208
to grid lead 202 and the grid of triode half 170a.
The power output amplifier 170 receives output of triode half 170a at plate
lead 210 which is directly coupled to grid lead 212 of second half triode
170b, and the cathode of triode 170b is connected for cathode follower
output via output lead 214.
The foregoing discloses a unique pre-amplifier design which melds the
latterday solid state electronics and its superlative logic capability
with the tried and true hard tube electronics which in some cases has been
found superior to that which solid state has to offer. In particular, it
has been found that the tonal characteristics of hard tube pre-amplifier
and amplifier circuitry is often times very desirable as compared to solid
state forms of a similar circuit. Therefore, the programmable circuitry
functions with the hard tube amplifier stages to produce multiple channels
of desirable sounding instrument signals while having the capability of
offering greater diversity as regards effects loops, footswitch mixing and
other synthesis modes of reproduction. The pre-amplifier also offers a
speaker contour filter for simulating diverse response characteristics.
Changes may be made in combination and arrangement of elements as
heretofore set forth in the specification and shown in the drawings; it
being understood that changes may be made in the embodiments disclosed
without departing from the spirit and scope of the invention as defined in
the following claims.
Top